1. Field of the Invention
This invention relates to the production of ozone for the sterilization of point of use potable water sources such as reverse osmosis systems, refrigerators, drinking fountains, etc.
2. Background of the Related Art
Ozone has long been recognized as a useful chemical commodity valued particularly for its outstanding oxidative activity. Because of this activity, it finds wide application in disinfection processes. In fact, it kills bacteria more rapidly than chlorine, it decomposes organic molecules, and removes coloration in aqueous systems. Ozonation removes cyanides, phenols, iron, manganese, and detergents. It controls slime formation in aqueous systems, yet maintains a high oxygen content in the system. Unlike chlorination, which may leave undesirable chlorinated organic residues in organic containing systems, ozonation leaves fewer potentially harmful residues. Ozone has also been shown to be useful in both gas and aqueous phase oxidation reactions that may be carried out by advanced oxidation processes (AOPs) in which the formation of hydroxyl radicals (OHxe2x80xa2) is enhanced by exposure to ultraviolet light. Certain AOPs may even involve a catalyst surface, such as a porous titanium dioxide photocatalyst, that further enhances the oxidation reaction. There is even evidence that ozone will destroy viruses. Consequently, it is used for sterilization in the brewing industry and for odor control in sewage treatment and manufacturing. Ozone may also be employed as a raw material in the manufacture of certain organic compounds, e.g., oleic acid and peroxyacetic acid.
Thus, ozone has widespread application in many diverse activities, and its use would undoubtedly expand if its cost of production could be reduced. For many reasons, ozone is generally manufactured on the site where it is used. However, the cost of ozone generating equipment and poor energy efficiency of producing ozone has deterred its use in many applications and in many locations.
On a commercial basis, ozone is currently produced by the silent electric discharge process, otherwise known as corona discharge, wherein air or oxygen is passed through an intense, high frequency alternating current electric field. The corona discharge process forms ozone (O3) through the following reaction:
{fraction (3/2)}O2= greater than O3; xcex94Hxc2x0298=34.1 kcal
Yields in the corona discharge process generally are in the vicinity of 2% ozone, i.e., the exit gas may be about 2% O3 by weight. Such O3 concentrations, while quite poor in an absolute sense, are still sufficiently high to furnish usable quantities of O3 for the indicated commercial purposes. Another disadvantage of the corona process is the production of harmful nitrogen oxides (NOx). Other than the aforementioned electric discharge process, there is no other commercially exploited process for producing large quantities of O3.
However, O3 may also be produced through an electrolytic process by impressing an electric current (normally direct current (DC)) across electrodes immersed in an electrolyte, i.e., electrically conducting fluid. The electrolyte includes water which is dissociated by the electrolytic process into its respective elemental species, O2 and H2. Under the proper conditions, the oxygen is also evolved as the O3 species. The evolution of O3 may be represented as:
3H2O= greater than O3+3H2; xcex94Hxc2x0298=207.5 kcal
It will be noted that the xcex94Hxc2x0 in the electrolytic process is many times greater than that for the electric discharge process. Thus, the electrolytic process appears to be at about a six-fold disadvantage.
More specifically, to compete on an energy cost basis with the electric discharge method, an electrolytic process must yield at least a six-fold increase in ozone yield. Heretofore, the necessary high yields have not been realized in any foreseeable practical electrolytic system.
The evolution of O3 by electrolysis of various electrolytes has been known for well over 100 years. High yields up to 35% current efficiency have been noted in the literature. Current efficiency is a measure of ozone production relative to oxygen production for given inputs of electrical current, i.e., 35% current efficiency means that under the conditions stated, the O2/O3 gases evolved at the anode are comprised of 35% O3 by weight. However, such yields could only be achieved utilizing very low electrolyte temperatures, e.g., in the range from about xe2x88x9230xc2x0 C. to about xe2x88x9265xc2x0 C. Maintaining the necessary low temperatures, obviously requires costly refrigeration equipment as well as the attendant additional energy cost of operation.
Ozone is present in large quantities in the upper atmosphere of the earth to protect the earth from the suns harmful ultraviolet rays. In addition, ozone has been used in various chemical processes and is known to be a strong oxidant, having an oxidation potential of 2.07 volts. This potential makes it the fourth strongest oxidizing chemical known.
Because ozone has such a strong oxidation potential, it has a very short half-life. For example, ozone which has been solubilized in waste water may decompose in a matter of 20 minutes. Ozone can decompose into secondary oxidants such as highly reactive hydroxyl radicals (OHxe2x80xa2) and peroxyl radicals (HO2xe2x80xa2). These radicals are among the most reactive oxidizing species known. They undergo fast, non-selective, free radical reactions with dissolved compounds. Hydroxyl radicals have an oxidation potential of 2.8 volts (V), which is higher than most chemical oxidizing species including O3. Most of the OHxe2x80xa2 radicals are produced in chain reactions where OHxe2x80xa2 itself or HO2xe2x80xa2 act as initiators.
Hydroxyl radicals act on organic contaminants either by hydrogen abstraction or by hydrogen addition to a double bond, the resulting radicals disproportionate or combine with each other forming many types of intermediates which react further to produce peroxides, aldehydes and hydrogen peroxide.
Electrochemical cells in which a chemical reaction is forced by added electrical energy are called electrolytic cells. Central to the operation of any cell is the occurrence of oxidation and reduction reactions which produce or consume electrons. These reactions take place at electrode/solution interfaces, where the electrodes must be good electronic conductors. In operation, a cell is connected to an external load or to an external voltage source, and electric charge is transferred by electrons between the anode and the cathode through the external circuit. To complete the electric circuit through the cell, an additional mechanism must exist for internal charge transfer. This is provided by one or more electrolytes, which support charge transfer by ionic conduction. Electrolytes must be poor electronic conductors to prevent internal short circuiting of the cell.
The simplest electrochemical cell consists of at least two electrodes and one or more electrolytes. The electrode at which the electron producing oxidation reaction occurs is the anode. The electrode at which an electron consuming reduction reaction occurs is called the cathode. The direction of the electron flow in the external circuit is always from anode to cathode.
Recent ozone research has been focused primarily on methods of using ozone, as discussed above, or methods of increasing the efficiency of ozone generation. For example, research in the electrochemical production of ozone has resulted in improved catalysts, membrane and electrode assemblies, flowfields and bipolar plates and the like. These efforts have been instrumental in making the electrochemical production of ozone a reliable and economical technology that is ready to be taken out of the laboratory and placed into commercial applications.
However, because ozone has a very short life in the gaseous form, and an even shorter life when dissolved in water, it is preferably generated in close proximity to where the ozone will be consumed. Traditionally, ozone is generated at a rate that is substantially equal to the rate of consumption since conventional generation systems do not lend themselves to ozone storage. Ozone may be stored as a compressed gas, but when generated using corona systems the output gas stream is essentially at atmospheric pressure. Therefore, additional hardware for compression of the gas is required, which in itself reduces the ozone concentration through thermal and mechanical degradation. Ozone produced by the corona process may also be dissolved in liquids such as water but this process generally requires additional equipment for introducing the ozone gas into the liquid, and at atmospheric pressure and ambient temperature only a small amount of ozone may be dissolved in water.
Because so many of the present applications have the need for relatively small amounts of ozone, it is generally not cost effective to use conventional ozone generation systems such as corona discharge. Furthermore, since many applications require the ozone to be delivered under pressure or dissolved in water, as for disinfecting, sterilizing, treating contaminants, etc., the additional support equipment required to compress and/or dissolve the ozone into the water stream further increases system cost.
Therefore, there is a need for an ozone generator system that operates efficiently on standard AC or DC electricity and water to deliver a reliable stream of ozone gas that is generated under pressure for direct use by the application. Still other applications would benefit from a stream of highly concentrated ozone that is already dissolved in water where it may be used directly or diluted into a process stream so that a target ozone concentration may be achieved. It would be desirable if the system was self-contained, self-controlled and required very little maintenance. It would be further desirable if the system had a minimum number of wearing components, a minimal control system, and be compatible with low voltage power sources such as solar cell arrays, vehicle electrical systems, or battery power.
A refrigerator is combined with an ozone generator water treatment system so that purified and disinfected water is available at an ice maker and/or water dispenser forming parts of the refrigerator. The water may be ozonated in a chilled treatment reservoir. Ozone may also be introduced up stream or down stream of the treatment reservoir to provide biofilm and microorganism control. Level and purity sensors are also provided for indicating the purified condition of the water.
The present invention relates to refrigerators supplied with either potable or purified water from which microorganisms can be eliminated using ozone.
Modem refrigerators are known which include a dispenser for dispensing chilled water and which further include an ice maker for dispensing ice cubes or ice chips. A wide variety of devices have been used to purify water, including particle filters, ultrafiltration, carbon filters, water softening systems, ion exchange systems, and reverse osmosis systems. In order to kill bacteria, viruses and other microorganisms, chlorine is commonly used. However, the chlorination of water is hazardous due to the formation of potentially harmful byproducts.
The present invention includes a water treatment system consisting of a carbon block, granulated activated carbon, reverse osmosis, and the like within or supplying a refrigerator to deliver chilled water to a dispenser, wherein the water has been treated with ozone prior to dispensing. The system of the present invention provides for generating ozone close by or within the refrigerator and engaging that ozone at one or more points in the water treatment system to control microbial growth either in the water conduits or on other water treatment devices that make up the water treatment system. The present invention integrates a water treatment system such as carbon block, granulated activated carbon, reverse osmosis, ozone generators and the like with a refrigerator to produce purified water that is free from microbial contamination.
One embodiment of the invention is defined by a refrigerator enclosure, a means of refrigerating the enclosure, a means for opening and closing the enclosure, an electrochemical ozone generator, a potable or purified water supply to the refrigerator, a means of connecting said water supply to the electrochemical ozone generator, a waste water discharge from the electrochemical ozone generator, and one or more connections to transfer ozone gas or ozonated water between the ozone generator and the potable or purified water stream. The potable or purified water stream is connected to the water inlet of the refrigerator and water from the potable or purified water stream is provided to an icemaker or a water dispenser for delivering microbial-free purified water. Water flowing through the water lines may be received under pressure, for example from a city water supply. The water stream may be subject to filtration processes such as carbon filtration, ultrafiltration or reverse osmosis. After passing through the treatment stages, the purified water may be held in a storage reservoir before delivery. Ozone gas or a liquid containing ozone may be introduced into this reservoir to provide disinfection and to provide odor and taste enhancement of the water before it is discharged. The water storage reservoir may serve as a chilled water supply. Care must be taken to avoid making the walls of this reservoir too thin to avoid freezing of the water in the reservoir. A sensor can be provided in the reservoir to avoid freezing.
Alternatively, or in combination with other embodiments of the invention, ozone gas may be introduced into the refrigerator compartments in order to control odor and maintain food freshness.
Water drains may also be provided from the aforementioned filtration devices to a common discharge point in the refrigerator since said filtration devices may produce reject water. The reject water lines may also be in communication with water rejected from the electrochemical ozone generator.
In addition to introducing ozone into the water storage reservoir, ozone as a gas or dissolved in liquid may be introduced up stream of the water filtration elements. The ozone which is introduced at these points serves to kill microorganisms including bacteria, viruses and protozoa, spores, and cysts, including attached biofilm microorganisms in the water treatment system. The ozone will maintain a clean condition of the filtration elements either membrane or carbon filtration. The electrochemical ozone generator may be in contact with the chilled refrigerator compartments. A wall may be used to separate it from either the chilling or freezing compartments. For example, the ozone generator may be in a walled compartment where at least one wall or a portion of the wall borders on the chill or freezer compartment. The thickness of the wall and physical properties of the wall are such to prevent freezing of the water in the electrochemical cell. However, the thickness is sufficient to allow heat transfer from the ozone generating cell through the enclosing wall to the chilled compartment. The ozone generating cell enclosure may be in physical connection with the chilled water storage reservoir to enable heat to pass from the ozone generator to the chilled water storage reservoir.
The water conduit from the source water inlet or the purified water stream to the electrochemical ozone cell contains a flow restriction device. Water that is contained in the electrochemical ozone cell cannot backflow and make contact with the inlet water stream. The backflow restriction device may include a check valve, which also guards against loss of pressure.
It is desirable for the refrigerator compartments to be chilled. The compartments will be at or close to the freezing point of water. The compartments may also be below the freezing point of water. It is desirable for the electrochemical ozone generator""s structural elements and the fluids contained inside the ozone generator to be at a temperature significantly above the temperature of the refrigerated compartments (10-20xc2x0 C.). However, it is desirable for the said ozone generator to be at a temperature below that normally encountered outside the refrigerator, e.g., room ambient air temperature. The invention utilizes the chilled compartments to maintain the cell temperature of the electrochemical ozone generator. This is accomplished by placement of the electrochemical cell in contact with or close to the wall of the chilled compartments. The desired temperature is maintained through use of a spacer material with defined heat conduction properties, typically a polymer. The spacer material regulates the heat transfer between the electrochemical ozone cell and the chilled compartment.